scholarly journals Temperature and Stress Dependence of Screw Dislocation Mobility in Nb-V-Ta Alloys Using Kinetic Monte Carlo Simulations

2021 ◽  
Vol 8 ◽  
Author(s):  
Xinran Zhou ◽  
Jaime Marian

In this work we present simulations of thermally-activated screw dislocation motion in Nb-Ta-V alloys for two distinct scenarios, one where kink propagation is solely driven by chemical energy changes, i.e., thermodynamic energy differences, and another one where a migration barrier of 1.0 eV is added to such changes. The simulations have been performed using a kinetic Monte Carlo model for screw dislocation kinetics modified for complex lattice-level chemical environments. At low stresses, we find that dislocation motion in the case with no barrier is controlled by long waiting times due to slow nucleation rates and extremely fast kink propagation. Conversely, at high stress, the distribution of sampled time steps for both kink-pair nucleation and kink propagation events are comparable, resulting in continuous motion and faster velocities. In the case of the 1.0-eV kink propagation energy barrier, at low stresses kink motion becomes the rate-limiting step, leading to slow dynamics and large kink lateral pileups, while at high stresses both kink pair nucleation and kink propagation coexist on similar time scales. In the end, dislocation velocities differ by more than four orders of magnitude between both scenarios, emphasizing the need to have accurate calculations of kink energy barriers in the complex chemical environments inherent to these alloys.

2010 ◽  
Vol 108 (1) ◽  
pp. 014905 ◽  
Author(s):  
P. W. May ◽  
J. N. Harvey ◽  
N. L. Allan ◽  
J. C. Richley ◽  
Yu. A. Mankelevich

Author(s):  
Vasily Bulatov ◽  
Wei Cai

The PN model discussed in the preceding chapter is a continuum approach that requires some atomistic input to account for non-linear interactions in the dislocation core. In this chapter, we introduce yet another continuum model that uses atomistic input for a different purpose. The kinetic Monte Carlo (kMC) model does not consider any details of the core structure but instead focuses on dislocation motion on length and time scales far greater than those of the atomistic simulations. The model is especially effective for diamond-cubic semiconductors and other materials in which dislocation motion is too slow to be observed on the time scale of molecular dynamics simulations. The key idea of the kMC approach is to treat dislocation motion as a stochastic sequence of discrete rare events whose mechanisms and rates are computed within the framework of the transition state theory. Built around its unit mechanisms, the kMC model simulates dislocation motion and predicts dislocation velocity as a function of stress and temperature. This data then can be used to construct accurate mobility functions for dislocation dynamics simulations on still larger scales (Chapter 10). In this sense, kMC serves as a link between atomistic models and coarse-grained continuum models of dislocations. The kMC approach is most useful in situations where the system evolves through a stochastic sequence of events with only a few possible event types. The method has been used in a wide variety of applications other than dislocations. For example, the growth of solid thin films from vapor or in solution is known to proceed through attachment and diffusion of adatoms deposited on the surface. Based on a finite set of unit mechanisms of the motion of adatoms, kMC models accurately describe the kinetics of growth and the resulting morphology evolution of the epitaxial films [95, 96, 97]. Similar kMC models have been applied to dislocation motion in crystals with high lattice resistance, such as silicon. In these materials, dislocations consist of long straight segments interspersed with atomic-sized kinks, depicted schematically in Fig. 9.1(a) as short vertical segments. As was explained in Section 1.3, dislocation motion proceeds through nucleation and migration of kink pairs and can be described well by a kMC model.


2020 ◽  
Vol 102 (3) ◽  
Author(s):  
Leonardo Evaristo de Sousa ◽  
Pedro Henrique de Oliveira Neto ◽  
Demetrio Antônio da Silva Filho

2019 ◽  
Vol 209 ◽  
pp. 133-143 ◽  
Author(s):  
Gustavo Leon ◽  
Nick Eaves ◽  
Jethro Akroyd ◽  
Sebastian Mosbach ◽  
Markus Kraft

2020 ◽  
Vol 32 (15) ◽  
pp. 155401 ◽  
Author(s):  
Shuai Chen ◽  
Junfeng Gao ◽  
Bharathi M Srinivasan ◽  
Gang Zhang ◽  
Viacheslav Sorkin ◽  
...  

Author(s):  
Lai MingRui ◽  
Ramanarayan Hariharaputran ◽  
Khoong Hong Khoo ◽  
Jin Hongmei ◽  
Shunnian Wu ◽  
...  

2019 ◽  
Vol 92 (10) ◽  
Author(s):  
Matthew J. Lloyd ◽  
Robert G. Abernethy ◽  
David E. J. Armstrong ◽  
Paul A. J. Bagot ◽  
Michael P. Moody ◽  
...  

Abstract A viable fusion power station is reliant on the development of plasma facing materials that can withstand the combined effects of high temperature operation and high neutron doses. In this study we focus on W, the most promising candidate material. Re is the primary transmutation product and has been shown to induce embrittlement through cluster formation and precipitation below its predicted solubility limit in W. We investigate the mechanism behind this using a kinetic Monte Carlo model, implemented into Stochastic Parallel PARticle Kinetic Simulator (SPPARKS) code and parameterised with a pairwise energy model for both interstitial and vacancy type defects. By introducing point defect sinks into our simulation cell, we observe the formation of Re rich clusters which have a concentration similar to that observed in ion irradiation experiments. We also compliment our computational work with atom probe tomography (APT) of ion implanted, model W-Re alloys. The segregation of Re to grain boundaries is observed in both our APT and KMC simulations. Graphical abstract


2006 ◽  
Vol 45 ◽  
pp. 522-529 ◽  
Author(s):  
Veena Tikare ◽  
Michael V. Braginsky ◽  
Didier Bouvard ◽  
Alexander Vagnon

An experimental validation of a 3D kinetic, Monte Carlo model for simulation of microstructural evolution during solid state sintering will be presented. The model – a statistical mechanical model, which can simulate curvature-driven grain growth, pore migration, and vacancy formation, diffusion and annihilation – is validated by comparing microstructural evolution obtained experimentally for a copper powder compact. The 3D microstructural evolution of copper powder particles sintering was imaged in-situ by microtomography. The images show particles with internal porosity percolating through the particles. Microstructural features – e.g., neck formation and growth – from the experimental images as well as the overall densification rates are compared to the simulations.


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